Merge pull request #1271 from n0rbed/rational

Simplifying fractions before solving

.typos.toml

@@ -1,4 +1,5 @@
 [default.extend-words]
 numer = "numer"
 Commun = "Commun"
-nd = "nd"
+nd = "nd"
+assum = "assum"

src/solver/main.jl

@@ -195,7 +195,7 @@ function symbolic_solve(expr, x::T; dropmultiplicity = true, warns = true) where
         for e in expr
             for var in x
                 if !check_poly_inunivar(e, var)
-                    warns && @warn("This system can not be currently solved by solve.")
+                    warns && @warn("This system can not be currently solved by `symbolic_solve`.")
                     return nothing
                 end
             end
@@ -276,7 +276,7 @@ function solve_univar(expression, x; dropmultiplicity=true)
         end
     end
 
-    subs, filtered_expr = filter_poly(expression, x)
+    subs, filtered_expr, assumptions = filter_poly(expression, x, assumptions=true)
     coeffs, constant = polynomial_coeffs(filtered_expr, [x])
     degree = sdegree(coeffs, x)
 
@@ -296,18 +296,28 @@ function solve_univar(expression, x; dropmultiplicity=true)
                 append!(arr_roots, og_arr_roots)
             end
         end
-
-        return arr_roots
     end
 
     if length(factors) != 1
-        for factor in factors_subbed
-            roots = solve_univar(factor, x, dropmultiplicity = dropmultiplicity)
+        for i in eachindex(factors_subbed)
+            if !any(isequal(x, var) for var in get_variables(factors[i]))
+                continue
+            end
+            roots = solve_univar(factors_subbed[i], x, dropmultiplicity = dropmultiplicity)
             append!(arr_roots, roots)
         end
     end
 
+    for i in reverse(eachindex(arr_roots))
+        for j in eachindex(assumptions)
+            if isequal(substitute(assumptions[j], Dict(x=>arr_roots[i])), 0)
+                deleteat!(arr_roots, i)
+            end
+        end
+    end
+
     if isequal(arr_roots, [])
+        @assert check_polynomial(expression) "This expression could not be solved by `symbolic_solve`."
         return [RootsOf(wrap(expression), wrap(x))]
     end
 

src/solver/preprocess.jl

@@ -40,16 +40,19 @@ function clean_f(filtered_expr, var, subs)
     unwrapped_f = unwrap(filtered_expr)
     !iscall(unwrapped_f) && return filtered_expr
     oper = operation(unwrapped_f)
+    assumptions = []
 
     if oper === (/)
         args = arguments(unwrapped_f)
         if any(isequal(var, x) for x in get_variables(args[2]))
-            return filtered_expr
+            filtered_expr = expand(args[1] * args[2])
+            push!(assumptions, substitute(args[2], subs, fold=false))
+            return filtered_expr, assumptions
         end
         filtered_expr = args[1]
         @info "Assuming $(substitute(args[2], subs, fold=false) != 0)"
     end
-    return filtered_expr
+    return filtered_expr, assumptions
 end
 
 """
@@ -238,15 +241,17 @@ julia> filter_poly((x+1)*term(log, 3), x)
 (Dict{Any, Any}(var"##247" => log(3)), var"##247"*(1 + x))
 ```
 """
-function filter_poly(og_expr, var)
+function filter_poly(og_expr, var; assumptions=false)
     expr = deepcopy(og_expr)
     expr = unwrap(expr)
     vars = get_variables(expr)
 
     # handle edge cases
     if !isequal(vars, []) && isequal(vars[1], expr)
+        assumptions && return Dict{Any, Any}(), expr, []
         return (Dict{Any, Any}(), expr)
     elseif isequal(vars, [])
+        assumptions && return filter_stuff(expr), []
         return filter_stuff(expr)
     end
 
@@ -256,14 +261,16 @@ function filter_poly(og_expr, var)
     # reassemble expr to avoid variables remembering original values issue and clean
     args = arguments(expr)
     oper = operation(expr)
-    new_expr = clean_f(term(oper, args...), var, subs)
+    new_expr, assum_array = clean_f(term(oper, args...), var, subs)
 
+    assumptions && return subs, new_expr, assum_array
     return subs, new_expr
 end
-function filter_poly(og_expr)
+
+function filter_poly(og_expr; assumptions=false)
     new_var = gensym()
     new_var = (@variables $(new_var))[1]
-    return filter_poly(og_expr, new_var)
+    return filter_poly(og_expr, new_var; assumptions=assumptions)
 end
 
 

test/solver.jl

@@ -57,9 +57,14 @@ end
 @variables x y z a b c d e
 
 @testset "Invalid input" begin
-    @test_throws AssertionError Symbolics.get_roots(x, x^2)
-    @test_throws AssertionError Symbolics.get_roots(x^3 + sin(x), x)
-    @test_throws AssertionError Symbolics.get_roots(1/x, x)
+    @test_throws AssertionError symbolic_solve(x, x^2)
+    @test_throws AssertionError symbolic_solve(1/x, x)
+end
+
+@testset "Nice univar cases" begin
+    found_roots = symbolic_solve(1/x^2 ~ 1/y^2 - 2/x^3 * (x-y), x)
+    known_roots = Symbolics.unwrap.([y, -2y])
+    @test isequal(found_roots, known_roots)
 end
 
 @testset "Deg 1 univar" begin